class Solution
{
    int dx[4] = { 0, 0, -1, 1 }, dy[4] = { 1, -1, 0, 0 };
    int m, n;
    bool vis[301][301];
public:
    int numIslands(vector<vector<char>>& grid)
    {
        m = grid.size(), n = grid[0].size();
        int ret = 0;
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == '1' && !vis[i][j])
                {
                    ret++;
                    bfs(grid, i, j);
                }
            }
        }
        return ret;
    }

    void bfs(vector<vector<char>>& grid, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i, j });
        vis[i][j] = true;

        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && y >= 0 && x < m && y < n && !vis[x][y] && grid[x][y] == '1')
                {
                    q.push({ x, y });
                    vis[x][y] = true;
                }
            }
        }
    }
};